Metal tank rectifier



ug- 4 1931.` `l?. a. sHANU 1,817,714

nur. TANK RGTIFIER Filed lag-ch 18, 1925 Patented Aug. 4, 1931 Vnaam. B. enum, or PITTSBURGH, PnNNsYLvANm, Assrenon ro waacrnmnousa:y

f morale a mNUr'AcfrUnINe COMPANY, A coBronArIoNorrENNsYLvANIA METAL TANK RECTIFIER Application med Iarch 18, 1925. erial No. 16,402.

My invention relates to vacuum devicesand rticuiarly to mercury-arc, metal-tank rectlrs. Y One of the greatest difiiculties met in metal- 5 tank mercury-arc rectifiers is the evacuation of vthe same, on account of the lar mass of metal involved and the diculty 1n freeing the walls 'of the rectifier-*from the occluded lo The process of evacuating such rectifiers,

a8 overs 1n the rectifier.

It is desirable, therefore, to ully utilize the effect of `pumping and evacuation, including the heat treatment for freeing occlude'd s, when the rectifier is first put into conition for o ration, and to avoid, if possible, repeat expensive 'evacuating processes when the rectifier is subsequently mounted in the piant where it is intended to operate. In certain cases, the'rectifier must be stored for a. feng-period of time, as during interruptions inoperatiomor while waiting. for ipment, or uring rthe process of shipment, and in such cases, the foregoing considerations with regard tothe maintenance of a high vacuum within the rectifier are of particular weight.

As far as I am aware, the preferred practice has been, heretofore, to hermetically close the evacuated metal-tank rectifier and to maintain itin `the evacuated condition during the periods when it wasnot operating. I have found that it is practically impossible 15o-maintain the Lvacuum in such metallic enclosing tanks for any considerableperiod of time.` The gases of the surrounding atmosphare slowly penetrate into `the interior of the tank, andthe ox gen, or water vapor, which enters the rectled, attacks the interior thereof, producing combinationsj which give much trouble lin the subsequent evacuation of the rectifier necessary to recommis` sion the same. r Y

l In accordance with m inventiomjI obvia'tethe difiiculties caus by the penetration of active gases into the rectifier, when left indefinitely' without pumping, byr filling the rectifier chamber with an inert gas, such as nitrogen, which is free from water vapor or other active gases, during the periods when the rectifier is not in operation, such as durlng shipping, storing, or service-interruptions. The inactive gas within the rectifier tank is preferably maintained at a pressure higher than the outer atmosphere, in order to positively prevent entrance of outer gases into t-he interior'of the tank. Whcn'the rectifier is again placed into operation, its pump is started,`which readily removes the inert gas, without involving the necessity for long treatment for removing occluded gases. The gaseous filling is thus only a temporary filling, which renders the apparatus substantially inoperativefor its intended purpose duringfits period of inactivity.

In theaccompanying drawing, the single figure of which is a diagrammatic view ofra y metal-tank rectifier installation in Vaccordance with a `preferred embodiment of my illi-A vention, a mercury-arc, metal-tank rectifier 1 is connected to amercury-vapor diffusion, or condensation pump, 2, which leads', through a valve 3, into an interstage reservoir, or vacuum tank, 4, from Awhich, the gases are pumped by means of a suitable motor,- driven fore-vacuum pump 5. A valve 6 is connected between the interstage reservoir 4 and the motor-driven pump 5.

' In modern mercury-arc rectifier installations, it is customary to produce a preliminary, or partial, vacuum in the interstage reservoir y means of a rotary pump, such as is shown at 5, and to operat-ea mercuryvapor pump between the rectifier andthe interstage reservoir for maintaining within the rectifier the high degree of vacuum which is absolutely essential forsuccessful operation. Both before theY rectifier is put into operation and during the first periodof its operation, both pumps usually work continuously in order to remove the gasesrgven of by the walls in the interiorof the ta The treatment of the rectifier during Athe initial formation period, prior to starting the operation, is ve difficult, and may rlast several weeks,` depen 'ng on the rate at which the relatively large massesof material inthe 00 interior of the tank can be freed from the occluded gases. Impurities in the Walls, oxi dation of the surface, and other minor defects, prolong this formation period, and may render its cost comparable With the cost of manufacture of the rectifier.

The firstV period of operation of the rectifier is the most critical, on account of fiashovers which result from' the evolution of gases resulting from the heating of the rectifier' by the operating current, and both vacuum pumps usually have to operate continuously for several months, in order to permit satisfactory operation, It is only after a relatively great amount of Work, and after a long time, that the rectifier is sufficiently treated to give satisfactory operation Without continuous operation of the forewacuum pump, which is then operated only intermittently, Whenever the vacuum in the interstage reservoir reaches too loW a value, but With the mercury-vapor vacuum pump operating continuously. After a still longer operating period, it may be found sufficient to operate both pumps only intermittently.

When the rectifier is removed from the test-floor in the place of manufacture, or When it is shut dovn for any considerable period of time, provision should be made to secure as much as possible of the benefit of the prior evacuation and treatment of the same. As pointed out above, hermetical enclosure of the rectifier during such periods does not prevent a gradual penetration of the surrounding gases into the interior, such gases usually containing oxygen and Water vapor and becoming occluded by the cold Walls, necessitating the repetition of initial treatment of the rectifier, prior to restoring it to operation.

According to my invention, instead of holding the tank evacuated, or, What may be even Worse, admitting the surrounding air thereto, during shut-doivn periods, I fill the interior of the rectifier with a gas Which is inactive with respect to the materials inside the rectifier. The gas Within the rectifier is preferably maintained at a pressure higher than the surrounding atmosphere in order to positively prevent the entrance of gases which may contain active ingredients such as Water vapor, oxygen, or the like, that may combine with the iron, or other substances, in the interior of the rectifier and render it very difficult, or at least require much time and expense, to properly exhaust the rectifier.

Any gas which does not enter into the combination With the interior surfaces of the rectifier and which is easily removed by pumping may be used. I have found that pure nitrogen is especially adaptable for the purposes of my invention since it is cheap and -it. can be very readily, and may be quickly, pumped from the interior of the rectifier when the operation of the same is to be re sumed.

Since commercial nitrogen usually contains some impurities, I preferably clean the same before filling it into the rectifier, by passing it in succession over hot copper to remove oxygen, copper oxide to remove hy drogen and calcium chloride and phosphorus pentoxide to remove Water vapor.

The valve 7 for enclosing the gas in the interior of the rectifier may be disposed either in the connect-ion between the rectifier and the mercury-vapor vacuum pump, or in the connection between either of the pumps and the interstage reservoir. In order tov fully preserve the effect of the prior evacuation, I preferably fill the inert gas into the entire vacuum system, including the rectifier l, the mercury-vapor vacuum pump 2 and the interstage reservoir 4, and, in such case, I may omit the valve. 3 in the connection between the mercury-vapor pump 2 and the inter stage reservoir 4, utilizing only a valve 7 at the exit from the interstage reservoir, which may be connected to any suitable nitrogen supply. To make such arrangement possible, I mount the rectifier tank l, thel mercuryvapor pump 2, the interstage reservoir l and the exit valve 6 of the interstage tank upon a common bedplate 8, in fixed relation to each other, as a single unit.

The advantages secured by my invention are not lost by the fact that the. vacuum system is occasionally disturbed While making repairs which require the opening of the tanks and admitting the outer atmosphere. Such periods can usually be made so short as to prevent any considerable deterioration of the interior of the rectifier, and, even in such cases, it is preferable to first fill the tanl; With an inactive gas which will penetrate into all pores prior to the admission of the outer atmosphere, thus creating a protective layer which will greatly facilitate the subsequent evacuation.

I claim as my invention:

l. A metal-tank mercury-arc rect-ifier hav ing internal surfaces, a valve for permitting the removal of gases from the interior of said rectifier, said rectifier interior surfaces being substantially free from occluded oxygen and Water vapor, and gas Within said rectifier which does not substantially affect the interior surfaces of said rectifier, said gas being at a pressure greater than that of the outer atmosphere.

2. A metal-tank mercury-arc rectifier having internal surfaces, a valve for permitting the removal of gases from the interior of said rectifier, said rectifier interior surfaces being substantially free from occluded oxygen and Water vapor, and substantially pure nitrogen gas Within said rectifier at a pressure greater than that of the outer atmosphere.

8. The method of handling and shipping to a slight diffusion of gas, shipping it, and

subsequently, at the close of said period of inactivity, causing nitrogen to be removed from said apparatus at the place of installation of said apparatus.

4. lThe method of handling and shipping a metal-tank electrical apparatus during a eriod of inactivity after said apparatus has n initially treated, including drying, which comprises filling said apparatus with a moisture-free gas at a pressure above the surrounding atmosphere, temporarily sealing the apparatus, said apparatus being subject to a slight diffusion of gas, shipping it, and subsequently, at the close of said period of inactivity, causing gas to be removed from said apparatus at the place of installation of said apparatus.

5. A mercury arc rectifier having internal surfaces, a closure means operable to permit the escape of gases from the interior of said apparatus, said interior surfaces of the apparatus being substantiallyfree from occluded Water vapor, and a filling of dry nitrogen Within said apparatus at a pressure above the surrounding atmosphere.

6. A mercury arc rectifier having internal surfaces, a closure means operable to permit the escape of gases from the interior of said apparatus, said interior surfaces of the apparatus being substantially free from occluded water vapor, and a filling of moisturefree gas within said apparatus at a pressure above the surrounding atmosphere.

7. A metal-tank electrical apparatus having internal surfaces, a closure means operable to permit the escape of gases from the interior of said apparatus, said interior surfaces of the apparatus being substantially free from occluded water vapor, and a filling of dry nitrogen within said apparatus at a pressure slightly above the surrounding atmosphere, during periods of inactivity, whereby an gas leakage which occurs is from the insi e out, rather than from the outside in, said filling rendering the apparatus substantially inoperative. i

8. A metal-tank electrical apparatusv havin internal surfaces, a closure means operab e to permit the escape of gases from the interior of said apparatus, said interior surfaces of the apparatus being substantially free from occluded water vapor, and a filling of moisture-free gas Within said apparatus at a pressure slightly above the surrounding atmos here, during periods of inactivity,

where any gas leakage which occurs is from the inslde out, rather than from the outside in, said filling rendering the apparatus substantially inoperative.

In testimony whereof, I have hereunto subscribed my nalne this 24th day of February,

ERROL B. SHAND. 

